DE69807192T2 - TOOL HOLDER FOR CUTTING INSERTS - Google Patents

Description

The present invention relates to an arrangement for fastening cutting inserts for the chip-forming processing of metals according to the preamble of claim 1.

Different cutting inserts and indexable inserts are mounted on tool holders in different, well-known ways. The most common way is that the insert has a central, through hole and that the insert pocket in the holder has a threaded hole. A locking or locking screw is screwed into the center hole of the insert and is screwed into the hole of the holder with suitable torque, and often a spacer with a central hole is placed between the insert and the base holding surface. Usually the insert pocket also has two internal, substantially vertical abutment surfaces or three abutment points for abutment against two of the insert side surfaces. The disadvantage with this construction is that after a period of use some play can easily occur. Another disadvantage is that the screw can easily be over-tightened, thereby damaging the screw or causing it to break.

Other known insert holders have a clamp or similar fastening arrangement that presses on the upper surface of the insert to clamp it in the insert pocket. The clamping force can be regulated by a screw. Such designs can be used, for example, to fasten cutting inserts that do not have a center hole, which is the case, among other things, when creating grooves in inserts and when splitting them.

In order to avoid play and generally to achieve a more stable mounting of a cutting insert, designs have been proposed in which the lower surface of the cutting insert and the bottom support surface of the insert pocket are formed as ribbed surfaces intended to fit together. Such designs are described in US-A-2,140,941 and US-A-2,453,464. A disadvantage with these designs, however, is that they require a considerable degree of grinding of the ribbed surfaces of either the cutting insert or the holder or both. A further disadvantage is that even if the insert has been fixed in a direction perpendicular to the ribs by means of a stop surface behind the insert, vertical play can occur with these designs as easily as with those with two completely flat abutment surfaces, particularly in machine operations with a tendency to vibration.

Furthermore, there are a number of disadvantages associated with the use of a stop surface for the insert behind this insert. For example, it is only possible to attach inserts that are precisely adapted to the length in question. Furthermore, the design of such a stop surface must The abutment surface must be adapted to the geometry of the insert. This surface must not, for example, damage the cutting edge, which in turn is turned away from the workpiece. Furthermore, such a stop surface can limit the accessibility of the insert and the holder to the workpiece to a certain extent.

A system for clamping inserts on a holder is described in WO-A-95/29026, which represents the closest prior art, the system being arranged to have parallel grooves on the underside of the insert and ribs on the holder, the ribs fitting into the grooves. The insert is screwed into the holder, creating a wedging action between the ribs and the grooves. This wedging and the friction between the flank surfaces of the ribs and grooves stabilize the insert to a considerable degree, even in a radial direction, but when cutting forces are large, this clamping is not entirely reliable and for this reason it is sometimes necessary to use a rear stop surface.

The primary object of the present invention is therefore to design a clamping system with an insert and a holder so that the use of a rear stop surface can be avoided.

A secondary object of the present invention is to design a clamping system in such a way that the same holder can accommodate different inserts with different basic geometries.

A third object of the invention is the optimization of the accessibility of the insert and the holder with respect to the workpiece.

A further object of the invention is the design of a clamping system which can optimally absorb both radial and axial cutting forces.

These and other objects and tasks are achieved or solved by the design of a clamping system in which such features are given as they are set out in claim 1.

To clarify, but not limit, the invention, an embodiment of the same will now be described in more detail with reference to the accompanying drawings. These are briefly summarized here:

Fig. 1 shows an insert and a holder according to the invention, seen directly from above.

Fig. 2 shows an insert and holder according to Fig. 1, seen directly from the side.

Fig. 3 shows a holder according to Figs. 1 and 2 separated without insert in perspective from obliquely above.

Fig. 4 shows the holder according to Fig. 3, directly from above.

Fig. 5 shows the holder according to Fig. 3, directly from the side.

Fig. 6 shows an insert according to the invention in perspective from above.

Fig. 7 shows the insert according to Fig. 6 directly from below.

Fig. 8 shows the insert according to Fig. 6 directly from the side.

Fig. 9 shows another insert according to the invention directly from above.

In Fig. 1 and 2, an insert is generally designated 1 and a holder is generally designated 2. The cutting insert is in most cases made of coated or uncoated cemented carbide. The geometry of the basic shape of the cutting inserts is not an essential feature of the invention, not least because one of the main objectives of the invention is that different inserts can be arranged in the same holder. Thus, the cutting insert according to Fig. 6 to 8 is an embodiment of the invention. However, it is characteristic of all the cutting inserts according to the invention that they have one or more grooves 3, the flank sides 3a, 3b of which act as contact surfaces for the flank surfaces 7a, 7b on an equivalent number of ribs 7. The grooves run mainly in the longitudinal direction of the holder 2 and/or mainly perpendicular to the axis of rotation of the workpiece. In Fig. 6 an insert is shown with only one groove 3, but the insert may also have several grooves (and the holder an equivalent number of ribs) according to the above-mentioned patent publication WO-A-95/29026. A substantially flat surface 4 adjoins the two sides of the grooves, which in the assembled state form an air surface, since a gap "s" (see Fig. 1 and Fig. 2) then exists between the surface 4 and the opposite, substantially flat bottom surface 5 in the holder. The gap or gap "s" may conveniently be between 0.02 and 0.03 mm. The flat surface 4 is delimited, inter alia, by four flanks 6 which extend mainly parallel to the grooves 3. In the same way as the flank surfaces of the grooves 3a, 3b, these flank surfaces 6 also act as support surfaces for the equivalent support surfaces 8 in the insert holder, which later form flank surfaces for the raised parts 9a, 9b in the holder. Consequently, when the insert is mounted, it rests only against the flank surfaces 7a, 7b and 8 of the holder. There is no contact between the tops of the ribs and the bottoms of the grooves, as shown by the gap "t" in Fig. 1. Suitable values for the angle of the flank surfaces 7a, 7b (or 3a, 3b) relative to the bottom surface have been found to be between 50º and 70º, preferably between 55º and 65º.

Because the insert rests only on the flanks 7a, 7b and 8, a clamping wedge function between the ribs and grooves is possible. In addition, the slight surface roughness of the directly pressed ribs has a positive effect on the clamping function. An important feature of the invention in question, however, is the aim of ultimately and permanently ensuring that the insert in radial direction, which is achieved by arranging flank or support surfaces 10 which are generally axial to the workpiece plus substantially perpendicular to the grooves 3. The support surfaces 10 are intended to lie against the opposing surfaces 11 in the tool holder. The mating surfaces 11, equivalent support surfaces 12 on the raised part 9b, are not intended to act as support surfaces, which is illustrated by the gap "u" in Fig. 2. The width of the flanks 10, which is limited by the protuberance of the flat surface, is accordingly somewhat narrower than the equivalent groove between the flank surfaces 11 and 12. A suitable size for the gap "u" is between 0.05 and 1 mm.

The insert shown in Figs. 6 to 8 has two operative cutting edges 13. After one cutting edge has been worn, the insert can be loosened and rotated half a turn to switch the other cutting edge forward. The insert is clamped in the holder by means of a locking screw, not shown, passed through the smooth hole 14 and is screwed into the threaded hole 15 in the holder. When the insert is switched, its other two flanks 10 act as bearing surfaces against the bearing surfaces 11 of the holder. As can be seen from Figs. 3 and 4, the threaded hole 15 in the holder is aligned with the rib 7. The reason for locating the hole on a rib instead of, for example, between two ribs is, of course, that the insert could break if subjected to a force between the two bearing lines. In cases where the insert has different ribs 7 to exert a symmetrical clamping force on the insert on both sides of the central rib, the insert and the holder are designed with an unequal number of grooves and ribs.

To improve cutting economy when machining with inserts according to this invention, these can also have a design with four operative cutting edges 13 as shown in Fig. 9. This insert can rest against the holder as shown in Figs. 3 to 5 in the same way as the insert shown in Figs. 6 to 8. One groove 3 receives the rib 7 of the holder, while the groove 3', which runs at right angles to this groove, is empty and open against the bottom surface 5. Some of the flank surfaces 10 (for example those designated 10 in Fig. 9) act as support surfaces against the support surfaces 11 of the holder, while the four flank surfaces 6 act as support surfaces against the surfaces 8 of the insert holder. When the insert is turned a quarter turn, the surfaces 6 and 10 change position with each other and the groove 3' receives the rib 7.

A number of advantages are achieved by the axially aligned, interactive or mutually acting support surfaces 10 and 11. The size and shape of different inserts need not have an influence on the design of the holder, because the holder does not have a rear support surface for the insert. In other words, you get a greater degree of freedom when designing an insert. With these inserts, it can also be difficult to design a functionally acceptable support surface, for example because of the different radial elevations and depressions. In addition, the holders can be given a more compliant or flexible and slimmer shape without any abutment surfaces behind the insert.

As mentioned above, the insert according to the invention in question is designed and equipped to absorb both radial and axial forces. Taking this into account, it should finally be noted that the design of the double-working inserts according to Figs. 6 to 8 is advantageous. Due to the straight front edge 13 on these inserts and the curved side edges 16 which adjoin on both sides, this insert can be used for facing and even for axial copying as well as for turning radii. Therefore, a large number of different contours can be produced.

Claims (5)

1. An arrangement for fastening a cutting insert (1) on an insert holder (2) for the machining of metal, the bottom surface of the insert having one or more grooves (3) extending substantially in the longitudinal direction of the holder and/or substantially at right angles to the workpiece rotation axis, the holding surface (5) of the holder being formed with one or more equivalent ribs (7) intended to fit into the grooves (3), characterized in that the cutting insert is made of uncoated or coated cemented carbide, that the bottom surface of the insert also has primary support surfaces (10) extending substantially at right angles to the grooves (3), and the holder has secondary support surfaces (11) extending substantially at right angles to the ribs (7), whereby the primary support surfaces (10) are caused to bear against the secondary support surfaces (11). thereby enabling the insert to withstand radial cutting forces, and that the flank surfaces (3a, 3b, 7a, 7b) of the ribs and grooves plus also the surfaces of side flanks (6, 8) have an angle relative to the holder surface on the holder of between 50º and 70º. 2. Arrangement according to claim 1, wherein the underside of the insert, apart from one or more grooves (3), also has the side flank surfaces (6) which run substantially parallel to the grooves and are intended to rest against the equivalent side flank surfaces (8) on the holder. 3. Arrangement according to claim 1 and 2, wherein the insert in the holder rests only against the flank surfaces (3a, 3b) of the grooves and on the side flanks (6). 4. Arrangement according to one of the preceding claims, wherein the cutting insert also has one or more other grooves (3') which run substantially at right angles to the grooves (3). 5. Insert for chip-forming metal machining with a bottom surface formed with one or more mutually substantially parallel grooves (3), characterized in that the bottom surface also has flank surfaces (10) extending substantially at right angles to the grooves (3), the flank surfaces being intended to bear against equivalent flank surfaces on a holder to ensure that the insert can withstand radial cutting forces.